More information. The look like they are clawing, which means too much nitrogen and therefore base nutrient solution. Then again, what pH are you watering at. Could be a lockout problem. Purple stems are notoriously mag deficiency, however, your mid leaves are not showing interveniel chlorosis, so if you see yellowing between your veins on the older fan leaves then you know the pH in your soil has creeped down below 5.5 and you are having lockout issues. If I were you, I would run x3 gallons of water more than your pots size of water with a mild fertilizer solution through each plant and keep on watering at ph 6.2 for the next couple of weeks at a .6-.8 EC.
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